1. Field of the Invention
The present invention discloses a low oil sensor for use with internal combustion engines. More particularly, such an oil sensor finds application in small, four-cycle engines. A low oil level signal is sensed, generally in an oil sump, and communicated to a switch assembly coupled to an indicator circuit.
2. Prior Art
Oil level sensors are known in the art. However, they are characterized by cumbersome, difficult to assemble structures, which are susceptible to malfunction by failure of one or more of their complicated structural members. Further, the earlier apparatus are relatively insensitive to signal pressures, many do not provide positive disconnects, some are difficult to reset, and/or they are prohibitively expensive to manufacture.
U.S. Pat. No. 3,577,121--Wing discloses a brake fluid level switch assembly. The switch is illustrated in the open or reference condition with the fluid level in reservoir 34 in the figures. A low level oil condition is illustrated in reservoir 32 wherein diaphragm 60 has expanded allowing conductor switch 56 to contact housing 48 to close the contact circuit. An attendant is required to disassemble and reset the switch apparatus after the contact and circuit closure. The circuit in this particular disclosure has an electrically grounded cover 48 to energize signal light 78.
U.S. Pat. No. 3,964,079--Katagiri discloses a brake fluid reservoir with a fluid level indicator. The fluid reservoir is partitioned by a diaphragm into a liquid phase and a vapor phase portion with the diaphragm therebetween and movable in response to changes in the liquid level of the liquid phase portion. An operating rod is movably connected to the diaphragm and contacts a sensing means. The rod is movable to actuate the sensing means to open or close a circuit in response to movement of the diaphragm as a function of changes in the brake fluid level. The signal circuit may be either normally open or normally closed.
U.S. Pat. No. 3,333,259--Carothers, Jr., illustrates a vacuum operated oil level indicator. The indicator utilizes an indicator circuit with two series aligned switches. The first switch is manually closed by an operator to introduce a vacuum to control switch 24. Manual actuation of the first switch closes switch contacts 52, 54 and introduces a vacuum at a normal or adequate oil level to switch 24 which open contacts 44, 46 of the second switch. The second switch maintains indicator lamp 68 in a non-indicating mode. Inadequate oil in the oil reservoir communicates air to the vacuum reservoir maintaining diaphragm operator 40 in its reference mode with contacts 44, 46 closed. The air dissipates the vacuum, thus moving diaphragm 24 and closing the circuit to actuate indicator lamp 68.
U.S. Pat. No. 3,022,497--Tyner teaches a variable orifice dipstick assembly in cooperation with a signal circuit which is responsive to a low level liquid in a sump or reservoir. The device is particularly taught for use in an automobile engine with the dipstick inserted into the oil sump. The assembly includes a diaphragm actuator and a guide member in a housing. The diaphragm operator separates the cavity of the housing into two distinct chambers. Contacts are provided that are spring-biased and diaphragm-operable or responsive to close a circuit contact. The housing serves as a ground member within the electric circuit and must be insulated from at least the contact means extending through the housing assembly. In operation, manifold vacuum from the engine is communicated to a first chamber on one side of the diaphragm and atmosphere is provided to the second chamber on the opposite side of said diaphragm. A plunger-like apparatus and valve assembly extends through the housing and diaphragm to contact a spade plug externally of the housing and is also movable with a valve guide of the diaphragm operator. This assembly includes two biasing springs, one biases the diaphragm operator assembly and the second spring biases a pin with a valve head attached thereto and operable through the diaphragm operator. As described, the dipstick at full or adequate oil level provides a stop for communication of atmosphere or crankcase pressure to the first chamber, which is connected to manifold vacuum. At low oil levels, atmosphere (crankcase pressure) is communicated to the first chamber and reduces the vacuum. The diaphragm operator is biased to close the circuit thereby energizing a signal lamp through the network of pins and contacts within the housing.
A low oil sensor known in the art, is coupled to the oil sump of an internal combustion engine and is operable in response to a crankcase pressure signal to move a reset switch. The sensor and switch are a spring-biased diaphragm operated mechanism. The over-center spring and reset switch are displaced from the diaphragm and switch cavity.
Although it is known to utilize oil or fluid sensors in internal combustion engines, the known apparatus generally provide variable or fixed-rate springs and diaphragms with connecting rod-type apparatus to close circuits or short circuit operating means to prevent engine damage.